合成不對稱之複雜型N型多醣骨架以為酵素促進多樣化與功能性研究

Abstract

位於醣蛋白(glycoprotein)上之N型多醣(N-glycan)具有結構多樣化、位置異構物眾多並且在不同的生物機轉中具備特定功能之特性。然而N型多醣之異構物也具有難以個別分離與鑑定之特性，同時它們更加細節的作用機轉原理尚未被徹底了解。這方面主要肇因於缺乏有效取得均質(homogeneous)特定異構物樣本之方法，特別是對於結構不對稱之N型多醣。當前取得N型多醣樣本的方法主要為化學合成法或化學酵素合成(chemo-enzymatic synthesis)法。前者倚賴複雜的保護基轉換與繁瑣的中間體純化；後者的瓶頸則在於酵素的可得性、反應的轉換率不完全以及仍然需要適當的引介保護基以進行位置選擇的酵素反應。本研究內容在於開發一個改進的不對稱N型多醣樣本之合成策略。此策略的核心在於先透過化學合成取得一個較簡單的中間體，並透過這個中間體再進行酵素醣化以得到具有岩藻醣基(fucosyl)或是唾液酸基(N-acetylnuraminyl)之不對稱N型多醣。

N-glycans on glycoproteins are structurally diverse, containing numerous regio-isomers with different roles in biological processes, such as immune signaling and disease progressions. However, these isomers are difficult to distinguish and their detailed functions are still not well understood mainly due to the lack of effective methods for access to these structures in pure form. Current access to complex type N-glycans is mainly through chemical or chemo-enzymatic synthesis; the former involves complex protecting group manipulation and intermediate purification, and the later often encounters problems of enzyme availability, incomplete reaction and requires introduction of protecting groups to avoid unwanted enzymatic glycosylation. We have developed an improved strategy for asymmetric N-glycan assembly and diversification using a common and versatile core substrate without protecting group for selective enzymatic fucosylation and sialylation.